1. Field of the Invention
The present invention relates generally to a valve assembly apparatus and, more particularly, to such apparatus including an actuator and a ball type valve.
2. Description of the Related Art
Various types of valves are known in the prior art for throttling fluid flow therethrough. One type, a ball valve, employs a valve member having a spherical shape which is mounted for rotation in a spherical chamber. This spherical valve member, or "ball", generally defines a bore having an axis extending through the center of the sphere. By rotating the ball about an axis normal to the bore axis, the ends of the bore are brought into alignment with the inlet and outlet portions of the valve, thereby effecting the opening of the valve. Continued rotation of the ball about the rotational axis decreases the area of the bore that is exposed to the inlet and outlet portions, thereby reducing flow. Still further rotation positions the bore axis approximately perpendicular to the flow direction, thereby effecting closure of the valve.
In efforts to provide a degree of control over fluid flow through the valve, some valves have incorporated means for throttling the flow passageway through the valve. Usually, this throttling is accomplished by providing a tapered flow passageway or bore extending through the ball, or by reducing the area of the outlet passageway in relation to the area of the inlet passageway.
Examples of such prior art are found in the U.S. Pat. Nos. 3,542,337 and 3,542,338 of Scaramucci and the Franck U.S. Pat. No. 3,762,682.
According to the disclosure in the Lester U.S. Pat. No. 5,593,135, the disclosed valve configuration of the Lester valve strives to achieve a linear relationship between valve rotation and fluid flow. According to the patent, this is accomplished by a cylindrical bore extending almost through the spherical valving member and terminating in a spherically generated throttling wall which contains a generally oblong outlet aperture.
The ball valves of the U.S. Pat. No. 4,846,213 of Hutchins et al., U.S. Pat. No. 4,881,718 of Champagne and U.S. Pat. No. 4,936,547 of Obst as disclosed comprise particularly configured rotatable ball elements designed to achieve asserted beneficial results as the solutions of problems noted in the patents. The valves of Champagne and Obst show grooves located about the rotatable ball member which is said to control cavitation in the fluid flow (Champagne) or variable seating force of the rotatable valve member (Obst). The rotatable ball element of Hutchins et al. has V-shaped openings to accommodate mounting of the ball and associated valve stem at an angle, relative to the fluid flow axis, which facilitate ease of sterilization, cleanability and maintenance of the valve, with ready disassembly for interior access.
Ease of disassembly is also a feature in the disclosed ball valve assembly of Ytzen et al. U.S. Pat. No. 3,456,916. This allows for ready removal of the central valve member for replacement in the event that critical sealing surfaces become damaged or eroded.
Weinhold U.S. Pat. No. 4,027,698 discloses a valve with a generally spherical closure member having a particularly shaped projection into the bore of the rotatable closure member which serves to mate with an opening of the housing so that pressure on the outlet or load side of the valve may be relieved when the valve is in the closed position.
Many applications which presently employ valves to regulate flow could benefit from the capability of a ball valve to achieve a desired relationship of flow area to degree of valve actuation which is non-linear or which may vary in accordance with a prescribed modulation waveform. Known ball valves are not capable of achieving all of the desired features of fine control, modulation of flow area with degree of valve rotation, and adequate flow shutoff which are provided by arrangements of the present invention.